1. Field of the Invention
The technology described herein generally relates to reagent tubes designed to facilitate pipetting of small volumes of liquid from within, and more particularly to reagent tubes that are used in extracting microfluidic quantities of polynucleotides in solution following extraction from biological samples.
2. Description of the Related Art
The medical diagnostics industry is a critical element of today's healthcare infrastructure. At present, however, diagnostic analyses no matter how routine have become a bottleneck in patient care. There are several reasons for this. For example, many diagnostic analyses can only be done with highly specialist equipment that is both expensive and only operable by trained clinicians. Such equipment is found in only a few locations, and often there is just one in any given urban area. This means that most hospitals are required to send out samples for analyses to these locations, thereby incurring shipping costs and transportation delays, and possibly even sample loss or mishandling.
Understanding that sample flow breaks down into several key steps, it would be desirable to consider ways to automate or make efficient as many of these as possible. In one key step, a biological sample, once extracted from a patient, must be put in a form suitable for a processing and detection regime that typically involves using PCR to amplify a vector of interest. Once amplified, the presence or absence of the vector in the sample needs to be determined unambiguously. Preparing samples for PCR is currently a time-consuming and labor intensive step, though not one requiring specialist skills, and could usefully be automated. By contrast, steps such as PCR and nucleotide detection have customarily only been within the compass of specially trained individuals having access to specialist equipment.
Sample preparation is labor intensive in part because of the number of reagents required, and the need for multiple liquid transfer (e.g., pipetting) operations. Furthermore, a trend towards portable diagnostic instruments, or those that can be easily installed in almost any healthcare setting (without requiring a dedicated facility), has meant that the instruments are configured to analyze very small (microfluidic or smaller) volumes of polynucleotide-containing solutions. With such volumes, it becomes important to minimize sample loss—such as from liquid transfer operations—during sample preparation. Even a loss of a very small fraction of a processing volume could result in loss of a significant number of copies of target polynucleotide and thereby result in a concomitant loss of amplification and detection sensitivity and—potentially—a false negative diagnosis. A major source of loss of liquid samples and solutions is from incomplete pipetting, where a pipette attempts to suck an entire quantity of fluid from a container, but where some fraction of that quantity is retained in the container, such as on the interior surfaces.
Various interior surface features in reagent tubes have been described elsewhere. U.S. Pat. No. 4,466,740 describes an array of reaction vessels on a plate, wherein each vessel has a conical interior lower surface that is stepped so that a number of concentric ridges of increasing diameter span between the bottom of the vessel and the vessel at its maximum width. Such a shape of interior surface is likely to present an increased surface area on which solution may remain during pipetting, and are unlikely to effectively channel the solution towards the location of a pipette tip. U.S. Pat. No. 6,143,250 (the '250 patent) describes liquid storage vessels having “ditches” in their lower interior surfaces that follow the interior surface of an inclined edge of the vessel. Although the '250 patent suggests that these grooves can be present in numbers of greater than two, and arranged radially with respect to the center of the vessel, such a configuration has at least the drawback that it would require a complex manufacture of the vessel, and are therefore limited to particular vessels, not necessarily those that are used in routine laboratory processes, such as biological sample preparation.
There is therefore a need for a method and apparatus of carrying out sample preparation on samples, so that loss of liquid volumes during liquid transfer is reduced. Such methods and apparatus could also find application to liquid transfer operations used in other fields, where mitigation of sample loss during work-up is important.
The discussion of the background herein is included to explain the context of the inventions described herein. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge as at the priority date of any of the claims.
Throughout the description and claims of the specification the word “comprise” and variations thereof, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.